Working with chroot environment

By Sachin

February 25, 2013

This post covers what/why chroot? and also steps to create chroot
environment.

As its man page says, “it is used to run commands or an interactive
shell with special root directory”. It provides an environment to
test new packages in a secured way without touching an actual system.
It can be called as a virtual system with isolated root(/)

Why chroot environment ?

Suppose I have a new package to test and compile with many
dependencies. Also I may have to compile each and every dependent
package till my requirement for the test-package is met. This process
can make my development machine highly unstable or sometime unusable,
this is certainly not I want. The best way I can deal with this is to
create a virtual machine, I can use
Qemu or
Virtual Box for that or I can make a
chroot environment in a separate directory and start working.
chroot environments are also used to host web-servers, so if at all
the web-server is compromised, not all the services are hampered and
the physical machine is still safe.

An advantage of having a chroot environment is the file-system is
totally isolated from the physical host. chroot has a separate
file-system inside the file-system, the difference is, it uses a newly
created root(/) as its root directory.

Building a chroot environment

For chroot, we need to create a file-system. The file hierarchy
within the directory is same as any other Linux file-system
such as /root, /usr, /etc, /bin, /opt etc.
We can make a Debian chroot environment using debootstrap or
rootstock, both are available for Ubuntu systems.
In this post I will use debootstrap to create a chroot
environment.

Install debootstrap using,

sudo apt-get install debootstrap

We can specify a system architecture, a suite(release name) and a
mirror to download from in the debootstrap parameter.

this will create a chroot environment for Ubuntu 12.04, from the
mirror.

chroot’ing

Once all the file are downloaded, we can chroot into
precise-chroot/ directory using

sudo chroot precise-chroot /bin/bash

where precise-chroot is the root directory, and the shell is
/bin/bash. You will be landed with the root prompt. Now you can
setup the package manager and update it. This will work same as any
other Linux environment.